1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of forming, on a semiconductor substrate, a photoresist pattern used for etching a highly reflective layer.
2. Description of the Related Art
As the integration and performance of semiconductor devices continues to increase, a higher level of technology is required to form the fine patterns necessary to produce such highly integrated and high performance semiconductor devices. The fine patterns of semiconductor devices are generally formed through a photolithography process. However, during photolithography, light reflected to a photoresist layer from a layer disposed beneath the photoresist layer causes the following problems.
First, it is difficult to produce a fine line width because a ripple is generated in the profile of the photoresist pattern due to a standing wave generated by the interference of light waves propagating in the photoresist layer. Although the ripple is removed during post-exposure baking, the photoresist pattern is undercut or is deformed so as to have the shape of a tail.
Second, although constant exposure energy is used, a swing effect occurs in which the amount of light absorbed by the photoresist layer varies according to the thickness of the photoresist layer. The swing effect also occurs due to the interference of light waves in the photoresist layer. The swing effect makes it difficult to produce a fine line width within a required range.
Third, notching or bridging is produced in the photoresist pattern by light reflecting from the region of a step in an underlayer, i.e., a layer produced beneath the photoresist pattern during the manufacture of the semiconductor device.
FIGS. 1 and 2 illustrate a conventional manufacturing process in which these problems are likely to arise.
Referring first to FIG. 1, an underlayer 52 having a step difference is formed on a semiconductor substrate 50. A highly reflective layer 54 having a high refractive index, such as a transparent insulating film, is formed on the underlayer 52. A photoresist layer 56 is coated on the highly reflective layer 54. Light 62 produced by exposure equipment (not shown) is passed through a mask 60, having a light blocking layer 58, in order to irradiate selected portions of the photoresist layer 56.
Referring now to FIG. 2, after the photoresist layer 56 is exposed through the process shown in FIG. 1, the photoresist layer 56 is developed to form photoresist patterns 64 and 66. The photoresist pattern 64 formed over a region of the underlayer 52 in which there is no step difference has a fine line width that is relatively uniform. However, the photoresist pattern 66 formed from that part of the photoresist layer 56 overlying the step difference in the underlayer 52 has a deformed line width pattern. This deformation is produced due to the interference of light waves 62 irradiating the highly reflective layer 54. When the deformation becomes severe, a notching or bridging defect, which is a critical defect in the fine line width pattern, is produced.
A conventional process has employed an anti-reflective coating (ARC) to combat these problems. FIG. 3 illustrates a conventional method of manufacturing a semiconductor device using such an anti-reflective coating (ARC).
In FIG. 3, reference numeral 68 denotes an ARC formed between the photoresist layer 56 and the highly reflective layer 54. In this case, the light reflected from the underlayer 54 and the ARC 68 to the photoresist layer 56 consists of the light e1, reflected from the interface between the ARC 68 and the photoresist layer 56, and the light e2, reflected from the interface between the highly reflective layer 54 and the ARC 68. The ARC can reduce the amount of reflected light e1+e2 reaching the photoresist layer 56 by ensuring that the phase difference between e1 and e2 is 180.degree. so as to give rise to destructive interference, or by absorbing almost all of the reflected light e1 or e2. In the former case the ARC is referred to as an interference type of ARC and in the latter case as an absorption type of ARC. A hybrid type of ARC having some of the characteristics of an interference type of ARC and an absorption type of ARC has also been developed.
The forming of such ARCs by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of hydrocarbon and helium has been disclosed in U.S. Pat. No. 5,569,501 issuing on Oct. 29, 1996 and entitled "Diamond-like Carbon Films Form Hydrocarbon Helium Plasma". In the PECVD method, an amorphous carbon layer is formed by controlling the temperature only under the substrate in a plasma chamber. However, this process is problematic in that the helium used as a carrier gas damages the anti-reflective coating during the generation of plasma or otherwise acts to limit the quality of the anti-reflective coating which can be produced.